The present invention relates to positive temperature coefficient (“PTC”) heaters used to vaporize insect control agents (e.g. repellents, insecticides, growth regulators), fragrances, and other air treatment chemicals (e.g. deodorizers) from an impregnated substrate. More particularly it relates to improved electrical contacts and structural assemblies for such devices.
A variety of electrical heaters have been developed on which, or through which, substrates impregnated with air treatment chemicals are placed. Heating of the substrate by such devices causes the air treatment chemical, such as allethrin, or any of various other commercially known vaporizable insecticides, to vaporize. While such devices can be powered by battery, they are typically designed to be plugged into electrical outlets.
A particularly preferred form of such electrical heaters uses a PTC heating element. However, such devices can experience some maintenance issues associated with the fragile nature of preferred PTC heating element materials and the structure of associated electrical contacts. In this regard, many PTC elements are somewhat fragile and their abutment with associated electrical contacts (particularly those that are stamped) can on occasion lead to breakage of the PTC element due to interaction of that element with an edge of the contact.
WO 2006/046209 (the disclosure of which is hereby incorporated by reference as if fully set forth herein) discloses a particularly desirable form of PTC electric heating device for vaporizing insecticides and fragrances impregnated in a solid mat. While this form of heater has many advantages, it still has some drawbacks.
For one thing, the electrical terminal/contact which has a pressure contact with the PTC heating element is a stamped part. As a result, there will occasionally be sharp edges formed on the contact. When these edges come into contact with the fragile PTC heater element, there can be an incidence of cracking of the PTC heater element, either when the electric heater device is being manufactured, shipped or handled, or as it heats and cools through use.
A variety of heating elements have been developed for these and analogous applications. See generally U.S. Pat. Nos. 4,037,082, 4,251,714, 4,635,026, 4,728,779, 4,814,584, 5,262,619, 6,192,169, 6,374,045, 7,012,222, and international publications WO 97/02054, WO 97/45008, and WO 98/57674; and European patent application EP 965 267. However, these were each deficient in some attribute.
Hence, a need still exists for improved PTC electrical heating devices useful for vaporizing air treatment chemicals.